Main magnetic properties required in a grain-oriented electrical steel sheet are iron loss, magnetic flux density and magnetostriction. When the magnetic flux density is high, the iron core can be improved using a magnetic domain control technology. As the magnetic flux density is higher, the magnetostriction becomes smaller and improved. Further, as the magnetic flux density is higher, an exciting current in a transformer can be made smaller and the transformer can be made smaller in size. From these points, improvement in magnetic flux density is important. Further, improvement in alignment to the Goss orientation (sharpening in the Goss orientation) in a secondary recrystallization texture contributes to improvement in magnetic flux density of the grain-oriented electrical steel sheet. For the improvement the sharpness of the Goss orientation, control of an inhibitor is important and therefore various studies have been made relating to the control of the inhibitor.
Further, methods of manufacturing a grain-oriented electrical steel sheet containing aluminum includes those called a complete solid-solution non-nitriding type, a sufficient precipitation nitriding type, a complete solid-solution nitriding type, and an incomplete solid-solution nitriding type depending on the controlling method of the inhibitor. Among them, the sufficient precipitation nitriding type is preferable from the viewpoint of facility protection and achievement of excellent magnetic properties. In this method, a slab is manufactured by continuous casting, then reheating of the slab, hot rolling, annealing, cold rolling, decarburization and nitration annealing, finish annealing and so on are performed. Conventionally, since the temperature of the slab reheating is about 1150° C., the slab is carried in a manner that the loss of heat energy is suppressed between the continuous casting and the reheating. Further, cooling of the slab down to room temperature is sometimes performed before the reheating in order to treat surface flaws of the slab.
However, in the conventional manufacturing method of the sufficient precipitation nitriding type, the control of the inhibitor cannot be performed sufficiently, failing to achieve excellent magnetic properties and causing break of the slab.